The present application relates to three-dimensional metal printing. It finds particular application with radiation imaging systems that comprise anti-scatter devices, including one-dimensional and/or two-dimensional anti-scatter grids, for example.
Radiographic imaging systems, such as computed tomography (CT) devices, for example, provide information, or images, of an object under examination or rather interior aspects of the object. For example, in radiographic imaging systems, the object is exposed to radiation, and one or more images are formed based upon the radiation absorbed by the object, or rather an amount of radiation that is able to pass through the object. Typically, highly dense objects absorb (e.g., attenuate) more radiation than less dense objects, and thus an object having a higher density, such as a bone or gun, for example, will appear differently than less dense objects, such as fatty tissue or clothing, for example.
A radiographic imaging system typically comprises a detector array and a radiation source respectively mounted on diametrically opposing sides of an examination region within which the object under examination resides. Radiation that traverses the object under examination is detected by one or more channels (also commonly referred to as pixels) of the detector array and respective signals are generated in response thereto. The signals are indicative of characteristics of the radiation that is detected by the respective channels and, thus, are indicative of the attenuation of the object from a particular view, or projection.
In an ideal environment, the radiation that is detected by a channel of the detector array corresponds to attenuated radiation that strikes the channel on a straight axis from a focal spot of the radiation source. This type of radiation is commonly referred to as primary radiation. However, due to inevitable interactions with the object and/or the imaging system, typically some of the radiation that is detected has deviated from the straight axis. Radiation that has deviated from the straight axis is commonly referred to as scattered radiation or secondary radiation. It will be appreciated that the detection of secondary radiation is undesirable because it can increase noise in a signal generated from the channel detecting the secondary radiation and/or it can reduce the quality of an image yielded from the signal.
In order to reduce the amount of secondary radiation that is detected by channels of the detector array, anti-scatter grids are commonly inserted between the examination region and the detector array. The anti-scatter grids are comprised of a plurality of anti-scatter plates or septa configured to absorb secondary radiation and a plurality of transmission channels configured to allow primary radiation to pass through the grid and be detected by a channel of the detector array. It will be appreciated that besides the aforementioned anti-scatter grid, other anti-scatter devices may be situated within the imaging system to absorb and/or attenuate radiation. For example, anti-scatter devices may be configured to mitigate the amount of radiation that escapes the examination region.
To absorb radiation, anti-scatter devices are generally comprised of high density metals, such as tungsten and/or molybdenum. Traditionally, 2D anti-scatter devices have been manufactured using casting techniques, which generally involve pouring a compound comprising liquid resin and metal particles into a mold (e.g., comprising a hollow cavity in the shape of the anti-scatter device being created). Once the resin has hardened, the anti-scatter device is removed from the mold. It will be appreciated that in some applications, an anti-scatter device is formed from multiple molds that produce layers of the anti-scatter device, where the layers are stacked on top of one another to form the anti-scatter device, once removed from the molds. For example, an anti-scatter grid may be tapered so as to define a channel having open ends that have different dimensions and/or that have dimensions that vary along the length of the channel. Accordingly, such an anti-scatter device may be made using a plurality of molds because the varying dimensions of the device may make it difficult to remove the device, as a single layer or element, from the mold and/or it may be difficult to flow the liquid resin into all of the different crevices of the mold, for example. In this situation, once the castings have hardened and been removed from the respective mold elements, the castings are precisely aligned and adhered together (e.g., using another liquid resin) to form the completed anti-scatter device (e.g., comprised of several layers of castings).
While current manufacturing techniques have proven useful in manufacturing 2D anti-scatter devices, the techniques are resource and time intensive. For example, precision alignment of the castings generally requires expensive machines and is time consuming. Moreover, the castings have to be polished to remove excess resin, particularly from the crevices between the layers). Thus, it would be beneficial to manufacture three-dimensional metal structures, and in particular three-dimensional anti-scatter devices, using non-casting techniques.